diff --git a/docs/changelog.rst b/docs/changelog.rst
index 9be9fe3ba..976479549 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -243,6 +243,8 @@ Detailed list of changes
 
 - Render block elements from the Unicode Symbols for Legacy Computing Supplement block (U+1CC00–U+1CEBF): separated block quadrants, separated block sextants, one sixteenth blocks, and one quarter block partial fills (:disc:`9849`)
 
+- Improve performance of using active process data when rendering the tab bar by only scanning processes once per second (:iss:`9862`)
+
 0.46.2 [2026-03-21]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/kitty/boss.py b/kitty/boss.py
index 829832432..b59bf3804 100644
--- a/kitty/boss.py
+++ b/kitty/boss.py
@@ -27,7 +27,7 @@ from weakref import WeakValueDictionary
 
 from kitty.types import WindowResizeDrag
 
-from .child import cached_process_data, default_env, set_default_env
+from .child import cached_process_data, default_env, process_data_cache, set_default_env
 from .cli import create_opts, green, parse_args
 from .cli_stub import CLIOptions, SaveAsSessionOptions
 from .clipboard import (
@@ -1923,6 +1923,13 @@ class Boss:
         if tm is not None:
             tm.mark_tab_bar_dirty()
 
+    def cache_process_data(self, enable: bool) -> None:
+        ' Turn on caching of process data. Must be called in enable/disable pairs. '
+        if enable:
+            self.process_data_cache_active = process_data_cache.start_caching()
+        else:
+            process_data_cache.stop_caching(self.process_data_cache_active)
+
     def update_tab_bar_data(self, os_window_id: int) -> None:
         tm = self.os_window_map.get(os_window_id)
         if tm is not None:
diff --git a/kitty/child-monitor.c b/kitty/child-monitor.c
index 9ce3d0b35..7f4b6685a 100644
--- a/kitty/child-monitor.c
+++ b/kitty/child-monitor.c
@@ -1001,6 +1001,7 @@ render(monotonic_t now, bool input_read) {
 
     const bool scan_for_animated_images = global_state.check_for_active_animated_images;
     global_state.check_for_active_animated_images = false;
+    call_boss(cache_process_data, "O", Py_True);
 
     for (size_t i = 0; i < global_state.num_os_windows; i++) {
         OSWindow *w = global_state.os_windows + i;
@@ -1021,6 +1022,7 @@ render(monotonic_t now, bool input_read) {
 
     }
     last_render_at = now;
+    call_boss(cache_process_data, "O", Py_False);
 #undef TD
 }
 
diff --git a/kitty/child.py b/kitty/child.py
index 1e3629549..0f361c799 100644
--- a/kitty/child.py
+++ b/kitty/child.py
@@ -8,6 +8,7 @@ from collections import defaultdict
 from collections.abc import Generator, Sequence
 from contextlib import contextmanager, suppress
 from itertools import count
+from time import monotonic
 from typing import TYPE_CHECKING, DefaultDict, Iterable, Mapping, Optional, TypedDict
 
 import kitty.fast_data_types as fast_data_types
@@ -96,27 +97,48 @@ def checked_terminfo_dir() -> str | None:
     return terminfo_dir if os.path.isdir(terminfo_dir) else None
 
 
-def processes_in_group(grp: int) -> list[int]:
-    gmap: DefaultDict[int, list[int]] | None = getattr(process_group_map, 'cached_map', None)
-    if gmap is None:
-        try:
-            gmap = process_group_map()
-        except Exception:
-            gmap = defaultdict(list)
-    return gmap.get(grp, [])
+class CachedProcessData:
+
+    cached_result: DefaultDict[int, list[int]] | None = None
+    cache_active: bool = False
+    cache_at: float = 0
+    ttl: float = 1
+
+    def process_group_map(self) -> DefaultDict[int, list[int]]:
+        if self.cached_result is None or not self.cache_active:
+            try:
+                self.cached_result = process_group_map()
+            except Exception:
+                self.cached_result = defaultdict(list)
+            self.cache_at = monotonic()
+        return self.cached_result
+
+    def processes_in_group(self, grp: int) -> list[int]:
+        return self.process_group_map()[grp]
+
+    def start_caching(self, refresh: bool = False) -> bool:
+        prev, self.cache_active = self.cache_active, True
+        if refresh or monotonic() - self.cache_at > self.ttl:
+            self.cached_result = None
+            self.cache_at = 0
+        return prev
+
+    def stop_caching(self, prev: bool) -> None:
+        self.cache_active = prev
+        self.cached_result = None
+
+
+process_data_cache = CachedProcessData()
+processes_in_group = process_data_cache.processes_in_group
 
 
 @contextmanager
 def cached_process_data() -> Generator[None, None, None]:
-    try:
-        cm = process_group_map()
-    except Exception:
-        cm = defaultdict(list)
-    setattr(process_group_map, 'cached_map', cm)
+    orig = process_data_cache.start_caching(refresh=True)
     try:
         yield
     finally:
-        delattr(process_group_map, 'cached_map')
+        process_data_cache.stop_caching(orig)
 
 
 def session_id(pids: Iterable[int]) -> int: